1. Field of the Invention
The subject of the invention relates to a process for obtaining a surfaced panel based on mineral fibers, particularly so-called insulating glass fibers. It applies particularly to the manufacture of soundproofing and/or thermal insulation panels comprising a covering on one face left exposed after assembly, for example such as panels for the ceilings of industrial or commercial premises.
Such a panel generally consists of a layer of mineral fibers, such as glass fibers bound by an organic binder onto which is glued on the exposed side, a layer of cladding intended to give it a decorative finished appearance. Depending on the desired degree of finish, the dampness of the rooms or the degree of soundproofing desired, this cladding layer is of the polyvinyl chloride film type, a skin of glass fibers perhaps painted to perfect its decorative appearance, an aluminum skin laid on cardboard and able to be covered with a coat of paint, or any other material known to this art.
Inasmuch as these panels serve as decor and even if their use is generally limited to rooms whose ceiling height is, for example, in excess of 10 meters, the appearance of the panel is particularly important, therefore the formation of unattractive creases must be particularly avoided. In addition, for a good lifespan of the material, it is also important to avoid any blistering where the cladding starts to come away. This condition therefore requires that the surface condition of the base layer be sufficiently smooth before gluing the cladding layer.
2. Description of the Related Art
However, as indicated earlier, this base layer is a layer of compressed glass wool, whose thickness is generally between 10 and 100 mm, inclusive. The process for obtaining this base layer is common to most insulating products in glass wool and comprises, for example and in a known manner, the following stages: glass in the molten state is continuously brought near to the peripheral wall of a centrifuge revolving at high speed in such a manner that under the effect of the centrifugal force, the molten glass is ejected through the orifices to the outside of the centrifuge in the form of radial filaments which are immediately drawn out into fibers by a gas current circulated in a ring at high speed and high temperature by a blowing crown placed just above the peripheral wall of the centrifuge, the gas current having a direction essentially perpendicular to the direction of filament emission. For basalt rock or slag based fibers, the so-called free centrifugation fiber forming process is preferably used. In both cases, the composition of size based on a thermosettable resin is sprayed onto the fibers which are then collected by a collection device consisting, for example, of an endless conveyor belt.
Even if one uses devices intended to make the fiber distribution uniform, the mattress obtained is never of rigorously constant thickness and some of the unevennesses created can be found on the finished product. In addition, the mattress of fibers is then taken to a forming device in which it is compressed and polymerization of the binder is initiated. Compression and conveyance of the mattress are obtained in a heated chamber with forced circulation of gas currents by means of two complementary calibrating conveyors formed, for example, of a succession of pallets hinged together and equipped with perforations for the smoke to pass through. In addition, given that in this forming stage it is desired to reduce the thickness of the mattress by a factor generally between 3 and 10, inclusive, these pallets must be sufficiently rigid to confer upon them a high mechanical strength enabling them to withstand the opposing pressure exerted by the mineral fiber mattress. It results from these different considerations that the dimensions of the pallets are mandatorily chosen within relatively narrow limits, the width being typically from 10 to 25 cm, inclusive. In addition, as the calibrating conveyors are of the endless belt type, there is always a degree of play between the pallets to allow their rotation. Also, due to wear of the pallets or simply the difficulty of very precise adjustment, the pallets are never accurately aligned and are therefore not all at the same height. On the finished product, these various irregularities result in marks in the form of steps. When applying the cladding, the effective gluing surface is limited to the "high" steps which does not enable satisfactory gluing and also, as the layers of cladding used are very thin, these "steps" are visible even on the finished product.
To remedy this defect, it is known that the surface of the mineral wool base layer can be rectified by planning to give it a smooth and even surface. However, this planning has major disadvantages. Firstly, it is not possible to effect this on line directly on the continuous belt delivered by the production installation, and secondly, during planning some of the thickness of the product, for example, 1 to 3 cm, inclusive, is removed which of course poses the problems of waste, but also deprives the panel of the mechanical reinforcement factor provided by the outer crust, always a little denser than the rest of the product.